Bipolar hypochlorite cell

ABSTRACT

Disclosed is a substantially vertical bipolar electrolytic cell especially suited to the production of alkali metal hypochlorites, divided into a plurality of cell units by horizontal partitions and featuring a bipolar electrode design wherein a foraminous, U-shaped cathode portion adapted to receive a sheet-like anode and a sheet-like anode portion are joined around a horizontal partition by a conductive portion.

Unite States Pate 1191 Bennett et a1.

[11] 3,849,281 1451 Nov. 19,1974

BIPOLAR HYPOCHLORITE CELL Inventors: John E. Bennett, Painesville; JamesW. Burkhardt, Mentor; Richard E. Loftiield, Chardon, all of Ohio DiamondShamrock Corporation, Cleveland, Ohio Filed: July 23, 1973 Appl. No.:381,730

Assignee:

US. Cl '204/268, 204/95, 204/269, 204/284 Int. Cl B0lk 3/04 Field ofSearch 204/95, 268, 269, 289, 204/286 References Cited UNITED STATESPATENTS 9/1906 Hinkson 204/268 1,541,947 6/1925 Hartman et a1 204/2683,676,315 7/1972 Goens et a1 204/95 3,779,889 12/1973 Loftfield 204/268Primary Examiner-John H. Mack Assistant Examiner-W. 1. Solomon Attorney,Agent, or FirmTimothy E. Tinkler 5 7] ABSTRACT Disclosed is asubstantially vertical bipolar electrolytic cell especially suited tothe production of alkali metal hypochlorites, divided into a pluralityof cell units by horizontal partitions and featuring a bipolar electrodedesign wherein a foraminous, U-shaped cathode portion adapted to receivea sheet-like anode and a sheetlike anode portion are joined around ahorizontal partition by a conductive portion.

6 Claims, 2 Drawing Figures 1 1| 1| eg/1 25 i ""7f 523 13 33- 11 31 92R? 1 BIPOLAR HYPOCHLORITE CELL BACKGROUND .OF THE INVENTION STATEMENT OFTHE INVENTION Therefore, it is an object of .the present invention toprovide a compact electrolytic cell for the production of hypochloritesat high current efficiencies.

This and further objects of the present invention will become apparentto those skilled in the art from the specification and claims thatfollow.

There has now been found an electrolytic cell comprising:

A. a substantially vertically disposed container having electrolyteinlet means in the lower portion thereof and electrolysis product outletmeans in the upper portion;

B. a plurality of horizontally disposed, electrically nonconductive,partitions dividing said container into a plurality of cell units;

C. a terminal, foraminous, sheet-like, monopolar anode horizontallydisposed in the first of said cell units; 7

D. a terminal, foraminous, monopolar cathode, horizontally disposed inthe last of said cell units and comprising a U-shaped constructionadapted to receive and encompass a foraminous, sheet-like anode;

E. means for impressing an electrolyzing current across said monopolarelectrodes;

F. at least one bipolar electrode comprising 1. a sheet-like,foraminous, anode portion,

2. a U-shaped, foraminous, cathode portion adapted to receive andencompass a sheet like anode, and

3. a conductive connecting portion joining said anode and cathodeportions;

G. said bipolar electrode being horizontally disposed in adjacent cellunits on opposite sides of a partitiion so that g 1. said anode portionis encompassed by a nextadjacent cathode and is parallel to saidpartition,

2. said cathode portion encompasses a nextship of two cathodes for eachanode created by the fact that each anode is encompassed by a U-shapedcathode. A further advantage relates to the long, useful life of thecell in continuous operation, at least in part due to the elimination ofgas-liquid interface corrosion (since the cell is operated in a floodedcondition). Ease of disassembly, replacement, and repair of componentparts when required is also found.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showingthe relationship between the electrodes and partitions of a cellaccording to the present invention.

FIG. 2 is a vertical cross-section of a typical cell of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Basically, the inventioncontemplates a vertically disposed electrolytic cell, divided byhorizontal partitions and employing bipolar electrodes that parallelopposite sides of said partitions, the positive ends of said electrodesbeing foraminous sheets and the negative, or cathodic ends, also beingforaminous and sheet-like but bent back on themselves to form a U-shapethat encompasses the next-adjacent anode sheet. Thus, each cell unitdefined by adjacent partitions contains a U- shaped cathode encompassinga sheet-like anode. Since the flow sequence ofelectrolyte and productsof electrolysis is from the bottom to the top of the entire cell, eachunit is operated in a substantially flooded condition.

The cells of the present invention may conveniently be used to producealkali metal, especially sodium and potassium, hypochlorites inconcentrations within the range of from I to 20 grams per liter by thedirect electrolysis of alkali metal chloride solutions, typicallyhavadjacent anode and is parallel to and spaced ing a concentration offrom 5 to I00 g/l. Since the problem of cathodic deposits when employingimpure alkali metal chloride solutions is well known, and in view of thefact that cells of the present invention contemplate two cathodes forevery anode, it is desirable to employ an alkali metal chloride feed ofhigh purity, thus avoiding the need for excessive backwashing or thelike. Conditions of operation are typical, for example involving a pH onthe order of 7 to 10, temperatures within the range of 5 to 50 C, etc.

The invention may be understood most readily by reference to theattached drawings wherein the vertical cell container is indicatedgenerally at l and is provided with electrolyte inlet means 3 near thebottom thereof and an outlet 5 in the upper portion for unreactedelectrolyte and products of electrolysis. The container 1 is dividedinto a plurality of cell units 7 by a plurality of electricallynonconductiv'e partitions 9. Materials of construction for both thecontainer and the partitions may be any mechanically sound, electricallynonconductive and corrosion resistant material, such as, polyvinylchloride, chlorinated polyvinyl chloride, Lucite, and the like. Eachpartition 9 joins with the four container walls in a substantiallysealing-engagement to prevent current and electrolyte leakage. Asexplained more fully hereinafter, one, and generally a corresponding,edge of each partition engages the container wall in such a manner as toaccommodate a bipolar electrode connecting portion. Each partition 9 isprovided with a means for passing electrolyte and products ofelectrolysis from the cell container bottom to its top through each unit7 in sequence. Typically and conveniently this means simply comprisesone or more holes 11 placed in diagonally opposite corners of partitions9 to provide a tortuous flow path, thus insuring adequate circulationand mixing with a minimum of current leakage.

In the first cell unit 7 is horizontally disposed a foraminousdimensionally stable monopolar terminal anode 13 connected to currentsupply means 15. Correspondingly, in the last cell unit 7" is ahorizontally disposed, foraminous, U-shaped, monopolar terminal cathodel7, spaced apart from partition wall 9 and connected to currentwithdrawal means 19. Thus, an electrolyzing current may be impressedacross current means 15 and 19. It will be readily apparent that thepolarity of the terminal electrodes in cell units 7and 7" may bereversed, that is, the monopolar anode 13 may be disposed in the lastcell unit 7". Further, it is not necessary that the first and last cellunits be defined by two adjacent partitions 9 since the first partitionand the bottom of the container can as well define the first cell unit7', with the last partition 9 and the cell container top defining thelast cell unit 7".

In the embodiments shown, the terminal anode 13 and terminal cathode 17are joined to current means 15 and 19 around a partition edge byconductive connecting portions 33 and 35, respectively. Otherarrangements, such as direct extension through container wall 29 toexternal current means are possible.

Intermediate the terminal electrodes is at least one bipolar electrodecomprising a foraminous, sheet-like,

anode portion 21, a U-shaped, foraminous, cathode portion 23 adapted toreceive and encompass a sheetlike anode, and a conductive connectingportion 25 joining said anode and cathode portions.

From the drawings, it will be seen that the U-shaped cathode portion 23of the bipolar electrode in the first cell unit 7' encompasses theterminal anode 13, both said terminal anode l3 and cathode portion 23being substantially parallel to the partitions 9 that form cell unit 7'.Cathode portion 23 is spaced apart from partitions 9, conveniently byspacing members 27 formed of an electrically insulating material. In thenext-adjacent cell unit 7, bipolar anode portion 21 is encompassed bycathode portion 23 of the next bipolar electrode in the series, bothagain being spaced apart from and horizon tal to partitions 9. It willbe understood that if only two cell units, e.g., cell units 7' and 7",are employed in the particular cell, anode portion 21 of the bipolarelectrode will be encompassed by terminal U-shaped cathode 17. At thispoint, it may be mentioned that the number of cell units, and hencebipolar electrodes, is limited only by practical mechanicalconsiderations and the desired production to be obtained from the entirecell, containers having from 2 to 25 cell units being typical.

The anode and cathode portions of each bipolar electrode are joined byelectrically conductive connecting portions 25 which are essentiallyperpendicular to the horizontally disposed anode and cathode portionsand are held between an edge of the partition 9, on opposite sides ofwhich said anode and cathode portions are disposed, and a containersidewall 29. Conveniently, and to insure a sealing (i.e., substantiallyliquid-tight) engagement, gasket 31 may be provided between wall 29 andpartition edge 9. Alternately, each partition edge may be slotted toreceive the connecting portion 25, any leakage resulting beingnegligible.

A variety of materials of construction for the bipolar electrodes arecontemplated. Generally, these will be dimensionally stable electrodes,necessarily foraminous to insure proper electrolyte circulation and gasrelease and essentially planar or sheet-like in configuration. The anodeportion may be of any conductive, resistant material bearing a coatingelectrocatalytic to the desired reaction, for example, expanded titaniummetal covered with a platinum group metal, platinum group metal oxide,or similar, known, coating. The cathodic portion must also haveappropriate physical and electrochemical characteristics and may be, forexample,

expanded titanium metal or palladium-titanium alloy (0.2 percent Pd),perforated stainless steel or nickel, or any of the foregoing or othermetals, coated with an electrocatalytic material (e.g., a platinum groupmetal) or uncoated. The connecting portion may be any conductive,corrosion resistant combination of the foregoing but need not beelectrocatalytic. For mechanical simplicity, the bipolar electrode maybe formed from a continuous sheet of expanded (e.g., titanium) metalbent to the appropriate S-shape", bearing an electrocatalytically active(e.g., platinum group metal oxide) coating on the anode portion andbeing uncoated on the cathode portion. On the other hand, the electrodemay be discontinuous in the sense that the anode portion may be coatedexpanded (titanium) metal butt welded to perforated stainless steelconnecting and cathodic portions. Other variations will suggestthemselves to those skilled in the art.

In order to maintain the minimum anode-cathode gap necessary forefficient operation, e.g.', 0.02().l, preferably about 0.03, inch,without the electrical short circuiting that would occur onanode-cathode contact, spacers to maintain this gap are suggested. Asimple and effective spacer may be comprised merely of a flexibleshoestring of inert polymer which may be interwoven in the foraminouselectrodes to maintain the gap without substantially interfering withelectrolyte circulation.

We claim:

1. An electrolytic cell comprising:

A. a substantially vertically disposed container having electrolyteinlet means in the lower portion thereof and electrolysis product outletmeans in the upper portion;

B. a plurality of horizontally disposed, electrically nonconductive,partitions dividing said container into a plurality of cell units;

C. a terminal, foraminous, sheet-like, monopolar anode horizontallydisposed in the first of said cell units;

D. a terminal, foraminous, monopolar cathode, horizontally disposed inthe last of said cell units and comprising a U-shaped constructionadapted to receive and encompass a foraminous, sheet-like anode;

E. means for impressing an electrolyzing current across said monopolarelectrodes;

F. at least one bipolar electrode comprising 1. a sheet-like,foraminous, anode portion,

2. a U-shaped, foraminous, cathode portion adapted to receive andencompass a sheet-like anode, and

3. a conductive connecting portion joining said anode and cathodeportions;

G. said bipolar electrode being horizontally disposed in adjacent cellunits on opposite sides of a partition so that 1. said anode portion isencompassed by a nextadjacent cathode and is parallel to said partition,

2. said cathode portion encompasses a nextadjacent anode and is parallelto and spaced apart from the opposite side of said partition and thenext-adjacent partition, and

3. said connecting portion is held between an edge of said partition anda container sidewall; and

H. means for passing electrolyte and products of electrolysis from thebottom to' the top of the container through the partition of each of thecell units in sequence.

2. A cell as in claim 1 wherein the bipolar electrode comprises acontinuous sheet of expanded titanium mesh, the anode portion of whichbears an electrocatalytic coating on the surface thereof.

3. A cell as in claim 1 wherein spacers are provided to space saidcathode and cathode portions apart from said partitions.

4. A cell as in claim 1 wherein spacers are provided between each anodeand its encompassing cathode to maintain an anode-cathode gap.

5. A cell as in claim 1 wherein a gasket is provided between saidcontainer sidewall and a partition edge so that the connecting portionof the bipolar electrode is held between said partition edge and saidgasket in a sealing arrangement.

6. A cell as in claim 1 wherein the bipolar electrode comprises an anodeportion of expanded titanium metal coated with an electrocatalyticmaterial and joined to connecting and cathode portions from the group offoraminous stainless steel, nickel, and palladium-titanium alloy.

1. AN ELECTROLYTIC CELL COMPRISING: A. A SUBSTANTIALLY VERTICALLYDISPOSED CONTAINER HAVING ELECTROLYTE INLET MEANS IN THE LOWER PORTIONTHEREOF AND ELECTROYLYSIS PRODUCT OUTLET MEANS IN THE UPPER PORTION B. APLURALITY OF HORIZONTALLY DISPOSED, ELECTRICALLY NONCOMDUCTIVE,PARTITIONS DIVIDING SAID CONTAINER INTO A PLURALITY OF CELL UNITS; C. ATERMINAL, FORAMINOUS, SHEET-LIKE, MONOPOLAR, ANODE HORIZONTALLY DISPOSEDIN THE FIRST OF SAID CELL UNITS; D. A TERMINAL, FORAMINOUS, MONOPOLARCATHODE, HORIZONTALLY DISPOSED IN THE LAST OF SAID CELL UNITS ANDCOMPRISING A U-SHAPED CONSTRUCTION ADAPTED TO RECEIVE AND ENCOMPASS AFORAMINOUS, SHEET-LIKE ANODE; E. MEANS FOR IMPRESSING AN ELECTROLYZINGCURRENT ACROSS SAID MONOPOLAR ELECTRODES; F. AT LEAST ONE BIPOLARELECTRODE COMPRISING:
 1. A SHEET-LIKE, FORAMINOUS, ANODE PORTION, 1.SAID ANODE PORTION IS ENCOMPASSED BY A NEXT-ADJACENT CATHODE AND ISPARALLEL TO SAID PARTITION,
 2. SAID CATHODE PORTION ENCOMPASSED ANEXT-ADJACENT ANODE AND IS PARALLEL TO AND SPACED APART FROM THEOPPOSITE SIDE OF SAID PARTITION AND THE NEXT-ADJACENT PARTITION, AND 2.a U-shaped, foraminous, cathode portion adapted to receive and encompassa sheet-like anode, and
 2. A U-SHAPED, FORAMINOUS, CATHODE PORTIONADAPTED TO RECEIVE AND ENCOMPASS A SHEET-LIKE ANODE, AND
 2. A cell as inclaim 1 wherein the bipolar electrode comprises a continuous sheet ofexpanded titanium mesh, the anode portion of which bears anelectrocatalytic coating on the surface thereof.
 2. said cathode portionencompasses a next-adjacent anode and is parallel to and spaced apartfrom the opposite side of said partition and the next-adjacentpartition, and
 3. said connecting portion is held between an edge ofsaid partition and a container sidewall; and H. means for passingelectrolyte and products of electrolysis from the bottom to the top ofthe container through the partition of each of the cell units insequence.
 3. A cell as in claim 1 wherein spacers are provided to spacesaid cathode and cathode portions apart from said partitions.
 3. ACONDUCTIVE CONNECTING PORTION JOINING SAID ANODE AND CATHODE PORTIONS;G. SAID BIPOLAR ELECTRODE BEING HORIZONTALLY DISPOSED IN ADJACENT CELLUNNITS ON OPPOSITE SIDE OF A PARTITION SO THAT
 3. a conductiveconnecting portion joining said anode and cathode portions; G. saidbipolar electrode being horizontally disposed in adjacent cell units onopposite sides of a partition so that
 3. SAID CONNECTING PORTION IS HELDBETWEEN AN EDGE OF SAID PARTITION AND A CONTAINER SIDEWALL; AND H. MEANSFOR PASSING ELECTROLYTE AND PRODUCTS OF ELECTROLYSIS FROM THE BOTTOM TOTHE TOP OF THE CONTAINER THROUGH THE PARTITION OF EACH OF THE CELL UNITSIN SEQUENCE.
 4. A cell as in claim 1 wherein spacers are providedbetween each anode and its encompassing cathode to maintain ananode-cathode gap.
 5. A cell as in claim 1 wherein a gasket is providedbetween said container sidewall and a partition edge so that theconnecting portion of the bipolar electrode is held between saidpartition edge and said gasket in a sealing arrangement.
 6. A cell as inclaim 1 wherein the bipolar electrode comprises an anode portion ofexpanded titanium metal coated with an electrocatalytic material andjoined to connecting and cathode portions from the group of foraminousstainless steel, nickel, and palladium-titanium alloy.